1. Field of the Invention
The present invention relates to an optical transmitter and receiver module, and particular to an integrated optical transmitter/receiver module.
2. Description of the Related Art
Recently, image information communications have been increasingly more common and attempts to adopt optical cables for communications have been made. Among these attempts, the access system optical communication adopts light waves of a wavelength band centered around 1.3 xcexcm for bidirectional communications between a plurality of subscribers and transmitter stations and at the same time, light waves of a wavelength band centered around 1.55 xcexcm for distributing image information from a transmitter station to the subscribers. In this type of system, it is necessary to install a WDM (Wavelength Division Multiplexing) optical transmitter and receiver module on the subscribers side of the system.
In the optical transmitter and receiver module, a type of module that employs a dielectric multilayer filter, that is, a reflective wavelength de-multiplexer, has received attention since the module realizes isolation over a broad bandwidth (Japanese patent application kokai 8-190026). As shown in FIG. 1, in a prior art optical transmitter and receiver module, single mode wave guides 2, 3, and 2xe2x80x2 each having a core contained in a cladding 12 made of quartz-based glass are formed on a silicon substrate 11. Near a position of intersection of wave guides 2 and 3, there is disposed a groove 4 formed with a dicing saw and a dielectric multilayer filter 5 is disposed therein. The optical axis of the wave guide 2xe2x80x2 formed opposite to the wave guides 2 and 3 of the dielectric multilayer filter 5 is in alignment with the optical axis of the wave guide 2.
In a planar light-wave circuit 30, an input/output single mode optical fiber 10A and an output single mode optical fiber 10B are fixedly inserted into a glass block 9. The glass block 9 is fixedly bonded to the end face of the circuit so that the optical axes of the input/output and output single mode optical fibers 10A and 10B are in alignment with the optical axes of the wave guides 2 and 3 respectively. Wavelength-multiplexed beams of light of wavelength bands centered around 1.3 xcexcm and 1.55 xcexcm are launched from the input/output port into the wave guide 2. The light beam of a wavelength band centered around 1.55 xcexcm is reflected at the dielectric multilayer filter 5 to be guided into the wave guide 3 and then is coupled into the single mode optical fiber 10B at the end of the wave guide to be outputted. On the other hand, the light beam of a wavelength band centered around 1.3 xcexcm from the wave guide 2 passes through the dielectric multilayer filter 5, i.e., the reflective wavelength multiplexer/de-multiplexer, and enters the wave guide 2xe2x80x2. The wave guide 2xe2x80x2 is divided into two at a Y branch 6 in which one of branching wave guide is connected to a laser diode 7 and the other is a photo-diode 8. The laser diode 7 is used for transmitting signals generated from one receiver of the subscribers to the input/output single mode optical fiber 10A, whereas the photo-diode 8 is used for converting the received optical signals into electric signals. Beams of light of a wavelength band centered around 1.55 xcexcm are used, for example, for distributing multi-channel video signals from a transmitter station to the subscribers, while beams of light of a wavelength band centered around 1.3 xcexcm are used in bidirectional communications for transmitting various kinds of data signals.
In the foregoing, there are projections and depressions on the side face of a groove 4 dug and formed with a dicing saw. Accordingly, it is difficult to grind the groove side faces. Moreover, a dielectric multilayer filter 5 is formed by alternately depositing plural layers of SiO2 and TiO2 on a polyimide film of a predetermined thickness so that the dielectric multilayer filter 5 transmits light waves of a wavelength band centered around 1.3 xcexcm and reflects a wavelength band centered around 1.55 xcexcm. In addition, the film of this dielectric multilayer filter is inserted into the groove and fixed with a silicone adhesive 13 and is subject to deterioration with age. Furthermore, there is a problem in that the projections and depressions of the side face of the groove, the adhesive agent, and the plastic film cause the beams of light passing therethrough a great deal of loss in the reflection and transmission.
Accordingly, the present invention has been made in view of the problem mentioned above, and its object is to provide an optical transmitter and receiver module, with less optical loss, which can be manufactured easily, and to provide the manufacturing method therefor.
The optical transmitter and receiver module according to the present invention for de-multiplexing a multi-wavelength optical signal into at least an optical signal of one wavelength band, and for receiving and transmitting the optical signal, said optical transmitter and receiver module comprising
input/output and output wave guides,
a transmit/receive wave guide,
a first substrate made of a cleavable crystal, having a cleavage plane, for supporting the input/output and output wave guides which intersect each other at a portion on the cleavage plane from which the input/output and output wave guides extend at an equal angle with respect to a normal line on said cleavage plane;
an interference filter in contact with said cleavage plane on the portion of intersection of the input/output and output wave guides of said first substrate; and
a second substrate made of the cleavable crystal having another cleavage plane in contact with said interference filter, for supporting a transmit/receive wave guide having receiver and transmitter wave guides which extend from a vicinity of said portion of intersection and are separated from each other.
In accordance with an aspect of the optical transmitter and receiver module of the invention, the first substrate has a second cleavage plane opposite to the cleavage plane having the portion of intersection on which the input/output and output wave guides terminate.
In accordance with another aspect of the optical transmitter and receiver module of the invention, the second substrate has another second cleavage plane opposite to the cleavage plane in contact with said interference filter on which the receiver and transmitter wave guides of the transmit/receive wave guide terminate.
In accordance with a further aspect of the optical transmitter and receiver module of the invention, the first and second substrate are made of InP, and the input/output and output wave guides and the transmit/receive wave guide are made of InGaAsP.
In accordance with a still further aspect of the optical transmitter and receiver module of the invention, the first and second substrate are made of GaAs, and the input/output and output wave guides and the transmit/receive wave guide are made of AlGaAs.
In accordance with another aspect of the optical transmitter and receiver module of the invention, the input/output and output wave guides and the transmit/receive wave guide are a channel-type three-dimensional wave guide.
In accordance with a further aspect of the optical transmitter and receiver module of the invention, the interference filter comprises a dielectric multilayer filter having a configuration for transmitting an optical signal of a shorter wavelength, and for reflecting an optical signal of a longer wavelength in the multi-wavelength optical signals.
In accordance with a still further aspect of the optical transmitter and receiver module of the invention, the optical transmitter and receiver module further comprises a photodetector and a light emitting device coupled to the receiver and transmitter wave guides of the transmit/receive wave guide respectively.
In accordance with another aspect of the optical transmitter and receiver module of the invention, the first and second substrates have anti-reflection coatings covering the second cleavage planes thereof respectively.
Furthermore, the manufacturing method of the optical transmitter and receiver module according to the present invention for de-multiplexing a multi-wavelength optical signal into at least an optical signal of one wavelength band, and for receiving and transmitting the optical signal, said method comprising
a wave guide formation process for forming, on a cleavage crystal substrate, input/output and output wave guides intersecting each other at a portion on a predetermined cleavage plane to be cleaved and extending from the portion of intersection at an equal angle with respect to a normal line at the portion of said cleavage plane, and a transmit/receive wave guide extending from a vicinity of said portion of intersection, the transmit/receive wave guide having receiver and transmitter wave guides being separated from each other;
a cleaving process for cleaving said cleavage crystal substrate in a direction of passing through the portion of intersection so as to form a first substrate for supporting said input/output and output wave guides having a cleavage plane at the portion of intersection and to form a second substrate having another cleavage plane for supporting the transmit/receive wave guide;
an interference filter formation process for covering, with an interference filter, at least a wave guide end face portion of at least one of the cleavage planes of said first substrate and said second substrate; and
a joint process for joining together of the cleavage planes of said first and second substrates by pinching said interference filter in order to allow said transmit/receive wave guide to extend from the vicinity of said portion of intersection.
In accordance with an aspect of the method of the invention, the wave guide formation process includes a step of cleaving said cleavage crystal substrate to generate a second cleavage plane opposite to the cleavage plane having the portion of intersection on the first substrate, the input/output and output wave guides terminating on the second cleavage plane.
In accordance with another aspect of the method of the invention, the wave guide formation process includes a step of cleaving said cleavage crystal substrate to generate another second cleavage plane opposite to the cleavage plane on the second substrate, the receiver and transmitter wave guides of the transmit/receive wave guide terminating on the second cleavage plane.
In accordance with a further aspect of the method of the invention, the wave guide formation process includes steps of forming a slab wave guide layer on said cleavage crystal substrate, forming a mask pattern showing a wave guide shape on the slab wave guide layer, etching the slab wave guide layer to form a ridge wave guide.
In accordance with a still further aspect of the method of the invention, the interference filter formation process includes a step of alternately depositing dielectric layers on the cleavage plane to form a dielectric multilayer filter having a configuration for transmitting an optical signal of a shorter wavelength, and for reflecting an optical signal of a longer wavelength in the multi-wavelength optical signals.
In accordance with another aspect of the method of the invention, the method further comprises a step of coating with anti-reflection coatings second cleavage planes opposite to the cleavage planes of the first and second substrates which are formed by cleaving said cleavage crystal substrate.
In accordance with a further aspect of the method of the invention, the joint process includes a step of bonding one of the first and second substrate onto a thermal conductive substrate with a first bonding material and a step of bonding another of the first and second substrate onto the thermal conductive substrate with a second bonding material having a lower melting point than a melting point of the first bonding material.
In accordance with a still further aspect of the method of the invention, the method further comprises a step of connecting the receiver and transmitter wave guides of the transmit/receive wave guide to a photodetector and a light emitting device respectively.
In accordance with another aspect of the method of the invention, the method further comprises a step of forming an elevated bump on the thermal conductive substrate beneath the photodetector and the light emitting device so as to align the optical axes of the receiver and transmitter wave guides to the photodetector and the light emitting device respectively.
In accordance with a further aspect of the method of the invention, the method further comprises a step of forming a concave-shaped portion depressed beneath the photodetector and the light emitting device on the thermal conductive substrate so as to align the optical axes of the receiver and transmitter wave guides to the photodetector and the light emitting device respectively.
According to the present invention, the wave guides and the substrate thereof are formed of a cleavable crystal of a compound semiconductor such as InP and InGaAsP. Accordingly, a de-multiplexing portion of the semiconductor wave guides are cut to cleave once and then the cleaved planes are coated with a dielectric multilayer film, that is, multilayer coating is carried out and thereafter the cleaved planes are joined together. Consequently, the processes are simplified and thus optical transmitter and receiver modules can be manufactured in a simple manner. Moreover, de-multiplexing is performed by the dielectric multilayer filter which is directly formed on the cleavage plane, thereby allowing for providing an improved environmental durability and reduced dependency on the environmental temperature of the de-multiplexing characteristics.